Method of making a thin film capacitor with an improved top electrode

ABSTRACT

A method of making a top electrode for a thin film capacitor with a multi-layer structure that includes a high dielectric oxide layer, a first conductive layer on the high dielectric oxide layer and having a high formability to a reactive ion etching, and a second conductive layer on the first conductive layer, the second conductive layer having a high formability to the reactive ion etching. The first conductive layer is deposited with a lower deposition rate than the second conductive layer wherein an interface between the first conductive layer and the high dielectric oxide layer is such that a density of a leak current across the interface is suppressed at not higher than 1×10 −8  A/cm 2  upon applying a voltage of 2V across the dielectric oxide layer after the multi-layer structure has been subjected to a heat treatment at 350° C.

This application is a division of Application Ser. No. 09/257,254, filedon Feb. 25, 1999, now U.S. Pat. No 6,291,290 the entire contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a thin film capacitor and a method offorming the same, and more particularly to a thin film capacitor with animproved top electrode suitable for advanced semiconductor devices andadvanced integrated circuits and a method of forming the same at highthroughput and high yield.

As a degree of integration of semiconductor memory devices such asdynamic random access memories has been on the increase, various kindsof high dielectric oxides such as (Ba, Sr)TiO₃ have been activelyinvestigated for a dielectric film of a thin film capacitor, instead ofsilicon dioxide or silicon nitride.

When the high dielectric oxide is used for the dielectric film of thethin film capacitor, a polysilicon electrode is not useable due to aproblem with possible oxidation of an interface of the polysiliconelectrode with the high dielectric oxide film, for which reason metalssuch as Pt, Ru and conductive metal oxides as well as conductivenitrides such as TiN have also been on the investigation for electrodesof the thin film capacitor.

The thin film capacitors having the high dielectric oxide layersandwiched between top and bottom electrodes have been investigated andreported mostly about improvements in capacitance characteristic andcurrent leakage characteristics both of which are important factors forthe thin film capacitors.

A prior art of the thin film capacitor was reported in Japanese Journalof Applied Physics, Vol. 36, No. 9B, pp. 5860-5865. The thin filmcapacitor has a Pt/(Ba, Sr)TiO₃/Pt structure, wherein a (Ba, Sr)TiO₃dielectric layer is deposited by a radio frequency magnetron sputteringmethod whilst Pt top and bottom electrodes are deposited by a DCsputtering method. There was investigated variations in current leakageof the thin film capacitor over deposition conditions for a second DCsputtering process for the Pt top electrode. It was confirmed that underapplication of a voltage of −1V. the leakage of current at a DC power of0.2 kW is smaller by two or three digits than at DC powers of 0.5 kW and1.0 kW. The reason why the leakage of current is reduced is that theroughness of an interface of the top electrode with the high dielectricoxide film reduces a Schottky barrier height of the interface betweenthe top electrode and the high dielectric oxide film.

However, prior art other than the above are directed to the highdielectric oxide layers and the bottom electrode structures whilst theprior art directed to the top electrode structure is a rare case. Thebottom electrode and the high dielectric oxide layer are likely to bestrongly influenced by later processes, for which reason most of thedevelopment and investigation was directed to the bottom electrode andthe high dielectric oxide layer. On the other hand, the top electrode isin major cases grounded, for which reason the top electrode has receivedweak attention or concern.

The present inventor has investigated possible various factors of thetop electrode which might provide influences to the thin film capacitorand could confirm the fact that an interface state between the highdielectric oxide layer and the top electrode provides large influencesto the current leakage characteristic and the adhesion between them forthe thin film capacitor

For example, the above first prior art thin film capacitor of theRu/(Ba, Sr)TiO₃/Ru structure shows the good leakage characteristic of1×10⁻⁸ A/cm². Notwithstanding, the first prior art thin film capacitorof the Ru/(Ba, Sr)TiO₃/Ru structure was placed in oxygen gas or nitrogengas at 500° C. for 30 minutes in order to have confirmed a temperaturehysteresis, whereby the leakage characteristic is deteriorated Thecauses of the deterioration in the current leakage characteristic hasbeen investigated with TEM observation and local EDX analysis and couldconfirm the fact that the deterioration in the current leakagecharacteristic is caused by both oxidation of Ru on an interface betweenthe Ru top electrode layer and the (Ba, Sr)TiO₃ high dielectric oxidelayer and a diffusion of Ru from the Ru top electrode layer into the(Ba, Sr)TiO₃ high dielectric oxide layer.

In general, the top electrode as formed receives a heat treatment suchas an anneal at a temperature of not less than 350° C. for formation ofinterconnections extending over the thin film capacitor or a passivationfilm overlying the thin film capacitor, for which reason if a highlyoxidizable metal or a highly diffusable metal is used for the topelectrode, then a thermal oxidation of the metal may appear whereby thecurrent leakage characteristic is deteriorated.

In order to improve the leak characteristics of the thin film capacitor,it is important to prevent the thin film capacitor from a later heattreatment at a high temperature of not less than 350° C. after the thinfilm capacitor has been formed. It was experimentally confirmed that,under condition of a low temperature heat treatment to be carried outafter the thin film capacitor has been formed, it is not problem toselect highly oxidizable and diffusable metals such as Ru or Ir for thetop electrode material and it is preferable to deposit such metal at alow power for prevention of any substantive deterioration in the leakcharacteristics of the thin film capacitor.

Meanwhile, the above second prior art shows the fact that the currentleakage characteristic could be improved by two or three digits by dropof a power of the DC sputtering process for reduction in depositionrate. Table 1 on page 5860 of Japanese Journal of Applied Physics showsthat in order to obtain the improvement by two or three digits of thecurrent leakage characteristic, it is required to remarkably reduce thedeposition rate of the top electrode down to about one quarter. Suchremarkable reduction in deposition rate causes an undesirable reductionin throughput, whereby productivity of the thin film capacitor is thusdropped.

An adhesiveness of the second prior art thin film capacitor of thePt/(Ba, Sr)TiO₃/Pt structure was evaluated and it was confirmed that theadhesiveness of the film is lowered by drop of the power applied to thetarget during the DC sputtering process. Such reduction in theadhesiveness of the film increases a probability of peeling the film,whereby reliability of the semiconductor device and the yield thereofare thus reduced.

Similarly to the case of Pt, the use of other materials such as Ru,RuO₂, kr and IrO₂ for the top electrode material also causes the sameproblem with drops in the deposition rate and the adhesiveness of thetop electrode even the drop of the sputter power may improve the currentleakage characteristics of the thin film capacitor.

In addition, Japanese laid-open patent publication No. 7-221197addresses a Ru bottom electrode for the thin film capacitor but issilent on the structure of the top electrode.

Further, Japanese laid-open patent publication No. 8-17806 addresses amethod of forming a thin film capacitor having the Pt/(Ba, Sr)TiO₃/Ptstructure but is silent on the structure of the top electrode and on anyinfluence to the capacitance characteristic by use of Pt for the topelectrode.

In the above circumstances, it had been required to develop a novel thinfilm capacitor with an improved top electrode structure which makes thethin film capacitor free form any problems and disadvantages asdescribed above and a novel method of forming the same.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a novelthin film capacitor with an improved top electrode structure which makesthe thin film capacitor free form any problems and disadvantages asdescribed above.

It is a further object of the present invention to provide a novel thinfilm capacitor with an improved top electrode structure free from theproblems with oxidation of an interface of the top electrode with a highdialectric oxide layer due to a heat treatment of not higher than 350°C.

It is a still further object of the present invention to provide a novelthin film capacitor with an improved top electrode structure free fromthe problems with diffusion of a metal of the top electrode into a highdielectric oxide layer due to a heat treatment of not higher than 350°C.

It is a further more object of the present invention to provide a novelthin film capacitor with an improved top electrode structure which allowthe thin film capacitor to keep excellent current leakage characteristiceven after a heat treatment has been carried out at a temperature of nothigher than 350° C.

It is still more object of the present invention to provide a novel topelectrode structure on a high dielectric oxide layer of a thin filmcapacitor, wherein the top electrode structure, makes the thin filmcapacitor free form any problems and disadvantages as described above.

It is moreover object of the present invention to provide a novel topelectrode structure on a high dielectric oxide layer of a thin filmcapacitor, wherein the top electrode structure is free from the problemswith oxidation of an interface of the top electrode with a highdielectric oxide layer due to a heat treatment of not higher than 350°C.

It is another object of the present invention to provide a novel topelectrode structure on a high dielectric oxide layer of a thin filmcapacitor, wherein the top electrode structure is free from the problemswith diffusion of a metal of the top electrode into a high dielectricoxide layer due to a heat treatment of not higher than 350° C.

It is still another object of the present invention to provide a noveltop electrode structure on a high dielectric oxide layer of a thin filmcapacitor, wherein the top electrode structure allows the thin filmcapacitor to keep excellent current leakage characteristic even after aheat treatment has been carried out at a temperature of not higher than350° C.

It is yet another object of the present invention to provide a novelmethod of forming a thin film capacitor for rising throughput of thethin film capacitor.

It is further another object of the present invention to provide a novelmethod of forming a thin film capacitor for improvement in adhesivenessof the films of the thin film capacitor.

It is an additional object of the present invention to provide a novelmethod of forming a thin film capacitor for improvement in yield of thefilms of the thin film capacitor.

It is a still additional object of the present invention to provide anovel method of forming a top electrode on a high electric oxide layerof a thin film capacitor for rising throughput of the thin filmcapacitor.

It is yet an additional object of the present invention to provide anovel method of forming a top electrode on a high electric oxide layerof a thin film capacitor for improvement in adhesiveness of the films ofthe thin film capacitor.

It is a further additional object of the present invention to provide anovel method of forming a top electrode on a high electric oxide layerof a thin film capacitor for improvement in yield of the films of thethin film capacitor.

It is also additional object of the present invention to provide a novelmethod of forming a top electrode on a high electric oxide layer of athin film capacitor for making the thin film capacitor free from theabove problems and disadvantages.

The first aspect of the present invention provides a multi-layerstructure comprising: a high dielectric oxide layer; a first conductivelayer on the high dielectric oxide layer, and processing a highformability to a reactive ion etching; and a second conductive layer onthe first conductive layer, and the second conductive layer processing ahigh formability to the reactive ion etching, wherein an interfacebetween the first conductive layer and the high dielectric oxide layeris such that a density of a leak current across the interface issuppresed at not higher than 1×10⁻⁸ A/cm² upon applying a voltage of 2Vacross the dielectric oxide layer after the multilayer structure hasbeen subjected to a heat treatment at 350° C.

The second aspect of the present invention provides a top electrodestructure of a thin film capacitor, the structure comprising: a firstconductive layer on a high dielectric oxide layer, and processing a highformability to a reactive ion etching; and a second conductive layer onthe first conductive layer, and processing a high formability to thereactive ion etching, wherein an interface between the first conductivelayer and the high dielectric oxide layer is such that a density of aleak current across the interface is suppressed at not higher than1×10⁻⁸ A/cm² upon applying a voltage of 2V across the dielectric oxidelayer after the multi-layer structure has been subjected to a heattreatment at 350° C.

The third aspect of the present invention provides a method of forming atop electrode on a high dielectric oxide layer of a thin film capacitor.The method comprises the steps of: carrying out a deposition of aconductive material having a formability to a reactive ion etching undera first deposition condition of a first deposition rate to deposit afirst conductive layer on the high dielectric oxide layer; andcontinuing the deposition the same conductive material under a seconddeposition condition of a second deposition rate which is higher thanthe first deposition rate to deposit a second conductive layer on thefirst conductive layer, wherein an interface between the firstconductive layer and the high dielectric oxide layer is such that adensity of a leak current across the interface is suppressed at nothigher than 1×10⁻⁸ A/cm² upon applying a voltage of 2V across thedielectric oxide layer after the multi-layer structure has beensubjected to a heat treatment at 350° C.

The fourth aspect of the presention provides a method of forming a topelectrode on a high dielectric oxide layer of a thin film capacitor. Themethod comprises the steps of: carrying out a first deposition of afirst conductive material having a formability to a reactive ion etchingunder a first deposition condition of a first deposition rate to deposita first conductive layer on the high dielectric oxide layer; andcarrying out a second deposition of a second conductive material havinga formability to the reactive ion etching under a second depositioncondition of a second deposition rate which is higher than the firstdeposition rate to deposit a second conductive layer on the firstconductive layer, wherein an interface between the first conductivelayer and the high dielectric oxide layer is such that a density of aleak current across the interface is suppressed at not higher than1×10⁻⁸ A/cm² upon applying a voltage of 2V across the dielectric oxidelayer after the multi-layer structure has been subjected to a heattreatment at 350° C.

The above and other objects, features and advantages of the presentinvention will be apparent from the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments according to the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a fragmentary across sectional elevation view illustrative ofa novel thin film capacitor with an improved top electrode in accordancewith the foregoing present inventions.

FIG. 2 is a fragmentary across sectional elevation view illustrative ofanother novel thin film capacitor with an improved top electrode inaccordance with the foregoing present inventions.

FIG. 3 is a fragmentary cross sectional elevation view illustrative of anovel thin film capacitor with an improved top electrode structure in afirst embodiment in accordance with the present invention.

FIG 4 is a fragmentary cross sectional elevation view illustrative of anovel thin film capacitor with an improved top electrode structure in afirst embodiment in accordance with the present invention.

FIG. 5 is a diagram illustrative of variations in density of leakcurrent of the novel thin film capacitor with the improved top electrodestructure and the conventional thin film capacitor.

FIG. 6 is a block diagram illustrative of a structure of a sputteringsystem as one example of the available sputtering systems for depositingthe electrodes of the novel thin film capacitor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first aspect of the present invention provides a multi-layerstructure comprising: a high dielectric oxide layer; a first conductivelayer on the high dielectric oxide layer, and processing a highformability to a reactive ion etching; and a second conductive layer onthe first conductive layer, and the second conductive layer processing ahigh formability to the reactive ion etching, wherein an interfacebetween the first conductive layer and the high dielectric oxide layeris such that a density of a leak current across the interface issuppressed at not higher than 1×10⁻⁸ A/cm² upon applying a voltage of 2Vacross the dielectric oxide layer after the multilayer structure hasbeen subjected to a heat treatment at 350° C.

The above novel thin film capacitor provides the following advantages.

First, the above novel thin film capacitor has the good electriccharacteristics. The material of the first conductive layer in contactwith the high dielectric oxide layer is deposited at a low depositionrate under a low deposition power to prevent reaction on the interfacebetween the first conductive layer and the high dielectric oxide layeror prevent the top surface of the high dielectric oxide layer fromreceiving any substantive damage.

Second, the top electrode structure makes it possible to shorten thetime for deposition of the top electrode for improvement in throughputof the thin film capacitor The first conductive layer is deposited at asufficiently low deposition rate for prevent the top surface of the highdielectric oxide layer from receiving any substantive damage, whilst thesecond conductive layer is deposited at a sufficiently high depositionrate for shortening a total time for depositions of the first and secondconductive layers.

Third, the first conductive layer intervening between the secondconductive layer and the high dielectric oxide layer prevents peeling ofthe top electrode from the high dielectric oxide layer for improvementin the yield of the thin film capacitor.

Fourth, the material of the first and second conductive layers are soselected as to have a high formability to a reactive ion etching. Theimprovement in formability of the top electrode allows a further scalingdown of the thin film capacitor with a highly accurate dimension,whereby a further increase in the degree of integration of thesemiconductor devices can be realized.

It is preferable that the first conductive layer and the secondconductive layer are made of the same conductive material which includesat least any one selected from the group consisting of Ru, RuO₂, Ir,IrO₂, and alloys thereof.

It is also preferable that the first conductive layer and the secondconductive layer are made of different conductive materials, each ofwhich includes at least any one selected from the group consisting ofRu, RuO₂, Ir, IrO₂, and alloys thereof because those materials have highformability to the reactive ion etching. This allows a furthersubstantive scaling down of the thin film capacitor 1 with a highaccurate dimension to be defined by the reactive ion etching. Thisfurther substantive scaling down of the thin film capacitor 1 allows anincrease in density of integration of the semiconductor devices andintegrated circuits.

It is further preferable that the first conductive layer consistsessentially of Ru and the second conductive layer consists essentiallyof Ir.

It is also preferable that the first conductive layer has a thickness ofabout one-tenth of a thickness of the second conductive layer. It isalso preferable that the first conductive layer has a thickness of aboutone-tenth of a thickness of the second conductive layer. It is notessential for the present invention to limit the thickness of the firstconductive layer in contact with the high dielectric oxide layer. It is,however, preferable that the first conductive layer is very thin. Thethickness of the first conductive layer is preferably not more than 10nanometers, and more preferably 5 nanometers. It is also not essentialfor the present invention to limit the thickness of the secondconductive layer separated from the high dielectric oxide layer. It is,however, preferable that the thickness of the second conductive layer isthicker by about ten times than the first conductive layer.

The second aspect of the present invention provides a top electrodestructure of a thin film capacitor, the structure comprising: a firstconductive layer on a high dielectric oxide layer, and processing a highformability to a reactive ion etching; and a second conductive layer onthe first conductive layer, and processing a high formability to thereactive ion etching, wherein an interface between the first conductivelayer and the high dielectric oxide layer is such that a density of aleak current across the interface is suppressed at not higher than1×10⁻⁸ A/cm² upon applying a voltage of 2V across the dielectric oxidelayer after the multi-layer structure has been subjected to a heattreatment at 350° C.

The above novel thin film capacitor provides the following advantages.

First, the above novel thin film capacitor has the good electriccharacteristics. The material of the first conductive layer in contactwith the high dielectric oxide layer is deposited at a low depositionrate under a low deposition power to prevent reaction on the interfacebetween the first conductive layer and the high dielectric oxide layeror prevent the top surface of the high dielectric oxide layer fromreceiving any substantive damage.

Second, the top electrode structure makes it possible to shorten thetime for deposition of the top electrode for improvement in throughputof the thin film capacitor. The first conductive layer is deposited at asufficiently low deposition rate for prevent the top surface of the highdielectric oxide layer from receiving any substantive damage, whilst thesecond conductive layer is deposited at a sufficiently high depositionrate for shortening a total time for depositions of the first and secondconductive layers.

Third, the first conductive layer intervening between the secondconductive layer and the high dielectric oxide layer prevents peeling ofthe top electrode from the high dielectric oxide layer for improvementin the yield of the thin film capacitor.

Fourth, the material of the first and second conductive layers are soselected as to have a high formability to a reactive ion etching. Theimprovement in formability of the top electrode allows a further scalingdown of the thin film capacitor with a highly accurate dimension,whereby a further increase in the degree of integration of thesemiconductor devices can be realized.

It is preferable that the first conductive layer and the secondconductive layer are made of the same conductive material which includesat least any one selected from the group consisting of Ru, RuO₂, Ir,IrO₂, and alloys thereof.

It is also preferable that the first conductive layer and the secondconductive layer are made of different conductive materials, each ofwhich includes at least any one selected from the group consisting ofRu, RuO₂, Ir, IrO₂, and alloys thereof because those materials have highformability to the reactive ion etching. This allows a furthersubstantive scaling down of the thin film capacitor 1 with a highaccurate dimension to be defined by the reactive ion etching. Thisfurther substantive scaling down of the thin film capacitor 1 allows anincrease in density of integration of the semiconductor devices andintegrated circuits.

It is further preferable that the first conductive layer consistsessentially of Ru and the second conductive layer consists essentiallyof Ir.

It is also preferable that the first conductive layer has a thickness ofabout one-tenth of a thickness of the second conductive layer. It isalso preferable that the first conductive layer has a thickness of aboutone-tenth of a thickness of the second conductive layer. It is notessential for the present invention to limit the thickness of the firstconductive layer in contact with the high dielectric oxide layer. It is,however, preferable that the first conductive layer is very thin. Thethickness of the first conductive layer is preferably not more than 10nanometers, and more preferably 5 nanometers. It is also not essentialfor the present invention to limit the thickness of the secondconductive layer separated from the high dielectric oxide layer. It is,however, preferable that the thickness of the second conductive layer isthicker by about ten times than the first conductive layer.

The third aspect of the present invention provides a method of forming atop electrode on a high dielectric oxide layer of a thin film capacitor.The method comprises the steps of: carrying out a deposition of aconductive material having a formability to a reactive ion etching undera first deposition condition of a fist deposition rate to deposit afirst conductive layer on the high dielectric oxide layer; andcontinuing the deposition the same conductive material under a seconddeposition condition of a second deposition rate which is higher thanthe first deposition rate to deposit a second conductive layer on thefirst conductive layer, wherein an interface between the firstconductive layer and the high dielectric oxide layer is such that adensity of a leak current across the interface is suppressed at nothigher than 1×10⁻⁸ A/cm² upon applying a voltage of 2V across thedielectric oxide layer after the multi-layer structure has beensubjected to a heat treatment at 350° C.

The above novel thin film capacitor provides the following advantages.

First, the above novel thin film capacitor has the good electriccharacteristics. The material of the first conductive layer in contactwith the high dielectric oxide layer is deposited at a low depositionrate under a low deposition power to prevent reaction on the interfacebetween the first conductive layer and the high dielectric oxide layeror prevent the top surface of the high dielectric oxide layer fromreceiving any substantive damage.

Second, the top electrode structure makes it possible to shorten thetime for deposition of the top electrode for improvement in throughputof the thin film capacitor. The first conductive layer is deposited at asufficiently low deposition rate for prevent the top surface of the highdielectric oxide layer from receiving any substantive damage, whilst thesecond conductive layer is deposited at a sufficiently high depositionrate for shortening a total time for depositions of the first and secondconductive layers.

Third, the first conductive layer intervening between the secondconductive layer and the high dielectric oxide layer prevents peeling ofthe top electrode from the high dielectric oxide layer for improvementin the yield of the thin film capacitor.

Fourth, the material of the first and second conductive layers are soselected as to have a high formability to a reactive ion etching. Theimprovement in formability of the top electrode allows a further scalingdown of the thin film capacitor with a highly accurate dimension,whereby a further increase in the degree of integration of thesemiconductor devices can be realized.

It is preferable that the first conductive layer is deposited at thefirst deposition rate by a first sputtering process with applying atarget with a first power and then the second conductive layer isdeposited at the second deposition rate by a second sputtering processwith applying the target with a second power which is higher than thefirst power.

It is also preferable that the first power is less than 1.7 W/cm², andthe second power is more than 1.7 W/cm². It is not essential for thepresent invention to limit the power level to be applied to the sputtertarget, but it is preferable to apply a low power level of, for example,1.7 W/cm² to the sputter target for a low rate deposition of the firstconductive layer in contact with the high dielectric oxide layer inorder to prevent the surface of the high dielectric oxide layer fromreceipt of any substantive damage. In this case, the thin film capacitorshows the good current leakage characteristics such that the leakcurrent density remains suppressed at not higher than 1×10⁻⁸ A/cm² underapplications to the target with the driving voltage in the range of 0Vto 2V. If, however, the sputter target is applied with a higher powerlevel than 1.7 W/cm² for a high rate deposition of the first conductivelayer in contact with the high dielectric oxide layer in order toprovide the surface of the high dielectric oxide layer from receipt ofany substantive damage, then the thin film capacitor shows theundesirable current leakage characteristics such that the leak currentdensity shows a rapid increase from 1×10⁻⁸ A/cm² as the driving voltageto be applied to the target is increased from 1.5V. Consequently, it ispreferable that the power level applied to the sputter target for a lowrate deposition of the first conductive layer in contact with the highdielectric oxide layer is suppressed at, for example, not higher than1.7 W/cm².

Namely, it is preferable that the first voltage level applied to thetarget for a low rate deposition of the first conductive layer is setnot higher than 1.7 W/cm², whilst the second voltage level applied tothe target for a high rate deposition of the second conductive layer issct higher than 1.7 W/cm².

For example, the first conductive layer and the second conductive layerare made of the same material such as Ru or Ir which has a highformability to the reactive ion etching. However, the first conductivelayer in contact with the high dielectric oxide layer is deposited at alow deposition rate by applying the sputter target with the low powerlevel of not higher than 1.7 W/cm², whilst the second conductive layerseparated from the high dielectric oxide layer is deposited at a highdeposition rate by applying the sputter target with the high power levelof higher than 1.7 W/Cm².

It is also preferable that the first and second conductive layers aredeposited by a chemical vapor deposition process under a firstdeposition condition and a second deposition condition.

It is also preferable that the first and second conductive layers aredeposited by an evaporation process under a first deposition conditionand a second deposition condition.

It is also preferable that the conductive material includes at least anyone of Ru, RuO₂, Ir, IrO₂, and alloys thereof because those materialshave high formability to the reactive ion etching. This allows a furthersubstantive scaling down of the thin film capacitor 1 with a highaccurate dimension to be defined by the reactive ion etching. Thisfurther substantive scaling down of the thin film capacitor 1 allows anincrease in density of integration of the semiconductor devices andintegrated circuits.

It is also preferable that the first conductive layer has a thickness ofabout one-tenth of a thickness of the second conductive layer. It isalso preferable that the first conductive layer has a thickness of aboutone-tenth of a thickness of the second conductive layer. It is notessential for the present invention to limit the thickness of the firstconductive layer in contact with the high dielectric oxide layer It is,however, preferable that the first conductive layer is very thin. Thethickness of the first conductive layer is preferably not more than 10nanometers, and more preferably 5 nanometers. It is also not essentialfor the present invention to limit the thickness of the secondconductive layer separated from the high dielectric oxide layer. It is,however, preferable that the thickness of the second conductive layer isthicker by about ten times than the first conductive layer.

The fourth aspect of the present invention provides a method of forminga top electrode on a high dielectric oxide layer of a thin filmcapacitor. The a top method comprises the steps of: carrying out a firstdeposition of a first conductive material having a formability to areactive ion etching under a first deposition condition of a firstdeposition rate to deposit a first conductive layer on the highdielectric oxide layer; and carrying out a second deposition of a secondconductive material having a formability to the reactive ion etchingunder a second deposition condition of a second deposition rate which ishigher than the first deposition rate to deposit a second conductivelayer on the first conductive layer, wherein an interface between thefirst conductive layer and the high dielectric oxide layer is such thata density of a leak current across the interface is suppressed at nothigher than 1×10⁻⁸ A/cm² upon applying a voltage of 2V across thedielectric oxide layer after the multi-layer structure has beensubjected to a heat treatment at 350° C.

The above novel thin film capacitor provides the following advantages.

First, the above novel thin film capacitor has the good electriccharacteristics. The material of the first conductive layer in contactwith the high dielectric oxide layer is deposited at a low depositionrate under a low deposition power to prevent reaction on the interfacebetween the first conductive layer and the high dielectric oxide layeror prevent the top surface of the high dielectric oxide layer fromreceiving any substantive damage.

Second, the top electrode structure makes it possible to shorten thetime for deposition of the top electrode for improvement in throughputof the thin film capacitor. The first conductive layer is deposited at asufficiently low deposition rate for prevent the top surface of the highdielectric oxide layer from receiving any substantive damage, whilst thesecond conductive layer is deposited at a sufficiently high depositionrate for shortening a total time for depositions of the first and secondconductive layers.

Third, the first conductive layer intervening between the secondconductive layer and the high dielectric oxide layer prevents peeling ofthe top electrode from the high dielectric oxide layer for improvementin the yield of the thin film capacitor.

Fourth, the material of the first and second conductive layers are soselected as to have a high formability to a reactive ion etching. Theimprovement in formability of the top electrode allows a further scalingdown of the thin film capacitor with a highly accurate dimension,whereby a further increase in the degree of integration of thesemiconductor devices can be realized.

It is preferable that the first conductive layer is deposited at thefirst deposition rate by a first sputtering process with applying atarget with a first power and then the second conductive layer isdeposited at the second deposition rate by a second sputtering processwith applying the target with a second power which is higher than thefirst power.

It is also preferable that the first power is less than 1.7 W/cm², andthe second power is more than 1.7 W/cm². It is not essential for thepresent invention to limit the power level to be applied to the sputtertarget, but it is preferable to apply a low power level of, for example,1.7 W/cm² to the sputter target for a low rate deposition of the firstconductive layer in contact with the high dielectric oxide layer inorder to prevent the surface of the high dielectric oxide layer fromreceipt of any substantive damage. In this case, the thin film capacitorshows the good current leakage characteristics such that the leakcurrent density remains suppressed at not higher than 1×10⁻⁸ A/cm² underapplications to the target with the driving voltage in the range of 0Vto 2V. If, however, the sputter target is applied with a higher powerlevel than 1.7 W/cm² for a high rate deposition of the first conductivelayer in contact with the high dielectric oxide layer in order toprovide the surface of the high dielectric oxide layer from receipt ofany substantive damage, then the thin film capacitor shows theundesirable current leakage characteristics such that the leak currentdensity shows a rapid increase from 1×10⁻⁸ A/cm² as the driving voltageto be applied to the target is increased from 1.5V. Consequently, it ispreferable that the power level applied to the sputter target for a lowrate deposition of the first conductive layer in contact with the highdielectric oxide layer is suppressed at, for example, not higher than1.7 W/cm².

Namely, it is preferable that the first voltage level applied to thetarget for a low rate deposition of the first conductive layer is setnot higher than 1.7 W/cm², whilst the second voltage level applied tothe target for a high rate deposition of the second conductive layer isset higher than 1.7 W/cm².

For example, the first conductive layer and the second conductive layerare made of the same material such as Ru or Ir which has a highformability to the reactive ion etching. However, the first conductivelayer in contact with the high dielectric oxide layer is deposited at alow deposition rate by applying the sputter target with the low powerlevel of not higher than 1.7 W/cm², whilst the second conductive layerseparated from the high dielectric oxide layer is deposited at a highdeposition rate by applying the sputter target with the high power levelof higher than 1.7 W/cm².

It is also preferable that the first and second conductive layers aredeposited by a chemical vapor deposition process under a firstdeposition condition and a second deposition condition.

It is also preferable that the first and second conductive layers aredeposited by an evaporation process under a first deposition conditionand a second deposition condition.

It is also preferable that the conductive material includes at least anyone of Ru, RuO₂, Ir, IrO₂, and alloys thereof because those materialshave high formability to the reactive ion etching. This allows a furthersubstantive scaling down of the thin film capacitor 1 with a highaccurate dimension to be defined by the reactive ion etching. Thisfurther substantive scaling down of the thin film capacitor 1 allows anincrease in density of integration of the semiconductor devices andintegrated circuits.

It is also preferable that the first conductive layer has a thickness ofabout one-tenth of a thickness of the second conductive layer. It is notessential for the present invention to limit the thickness of the firstconductive layer in contact with the high dielectric oxide layer. It is,however, preferable that the first conductive layer is very thin. Thethickness of the first conductive layer is preferably not more than 10nanometers, and more preferably 5 nanometers. It is also not essentialfor the present invention to limit the thickness of the secondconductive layer separated from the high dielectric oxide layer. It is,however, preferable that the thickness of the second conductive layer isthicker by about ten times than the first conductive layer.

FIG. 1 is a fragmentary across sectional elevation view illustrative ofa novel thin film capacitor with an improved top electrode in accordancewith the foregoing present inventions. A novel thin film capacitor 1 hasthe following structure. A bottom electrode layer 102 is provided on asemiconductor substrate 101. A high dielectric oxide layer 103 isprovided on the bottom electrode layer 102. A top electrode 105 isprovided on the high dielectric oxide layer 103. The top electrode 105further comprises a conductive layer 104 made of a single conductivematerial which shows a formability to a reactive ion etching. Theconductive layer 104 further comprises a first part 104 a which has beendeposited at a first deposition rate and a second part 104 b which hasbeen deposited on the first part 104 a at a second deposition rate whichis higher than the first deposition rate. The first part 104 a and thesecond part 104 b are made of the same conductive material but aredeposited at different deposition rates from each other so that thesecond deposition rate of the second part 104 b is higher than the firstdeposition rate of the first part 104 a. After the above thin filmcapacitor 1 having the top electrode layer 104 is subjected to a heattreatment at 350° C., the above thin film capacitor shows a good leakcurrent density characteristic such that the leak current densityremains suppressed at not higher than 1×10⁻⁸ A/cm² under application ofa driving voltage in the range of 0V to 2V.

It is preferable that the conductive layer 104 includes at least any oneof Ru, RuO₂, Ir, IrO₂, and alloys thereof because those materials havehigh formability to the reactive ion etching. This allows a furthersubstantive scaling down of the thin film capacitor 1 with a highaccurate dimension to be defined by the reactive ion etching. Thisfurther substantive scaling down of the thin film capacitor 1 allows anincrease in density of integration of the semiconductor devices andintegrated circuits.

The conductive layer 104 may be deposited by any one of a sputteringmethod, a chemical vapor deposition method and an evaporation method,provided that the second deposition rate of the second part 104 b ishigher than the first deposition rate of the first part 104 a.

When the sputtering method is applied to deposit the top electrode 105,the first part 104 a is deposited by applying a target with a firstpower and then the second part 104 b is deposited by applying the sametarget with a second power which is higher than the first power so thatthe second deposition rate of the second part 104 b is higher than thefirst deposition rate of the first part 104 a.

It is not essential for the present invention to limit the power levelto be applied to the sputter target, but it is preferable to apply a lowpower level of, for example, 1.7 W/cm² to the sputter target for a lowrate deposition of the first part 104 a in contact with the highdielectric oxide layer 103 in order to prevent the surface of the highdielectric oxide layer 103 from receipt of any substantive damage. Inthis case, the thin film capacitor shows the good current leakagecharacteristics such that the leak current density remains suppressed atnot higher than 1×10⁻⁸ A/cm² under applications to the target with thedriving voltage in the range of 0V to 2V. If, however, the sputtertarget is applied with a higher power level than 1.7 W/cm² for a highrate deposition of the first part 104 a in contact with the highdielectric oxide layer 103 in order to provide the surface of the highdielectric oxide layer 103 from receipt of any substantive damage, thenthe thin film capacitor shows the undesirable current leakagecharacteristics such that the leak current density shows a rapidincrease from 1×10⁻⁸ A/cm² as the driving voltage to be applied to thetarget is increased from 1.5V. Consequently, it is preferable that thepower level applied to the sputter target for a low rate deposition ofthe first part 104 a in contact with the high dielectric oxide layer 103is suppressed at, for example, not higher than 1.7 W/cm².

Namely, it is preferable that the first voltage level applied to thetarget for a low rate deposition of the first part 104 a is set nothigher than 1.7 W/cm², whilst the second voltage level applied to thetarget for a high rate deposition of the second part 104 b is set higherthan 1.7 W/cm².

For example, the first part 104 a and the second part 104 b are made ofthe same material such as Ru or Ir which has a high formability to thereactive ion etching. However, the first part 104 a in contact with thehigh dielectric oxide layer 103 is deposited at a low deposition rate byapplying the sputter target with the low power level of not higher than1.7 W/cm², whilst the second part 104 b separated from the highdielectric oxide layer 103 is deposited at a high deposition rate byapplying the sputter target with the high power level of higher than 1.7W/cm².

It is also preferable that a first thickness of the first part 104 a ismuch thinner than a second thickness of the second part 104 b. Forexample, the first thickness of the first part 104 a is about our, tenthof the second thickness of the second part 104 b.

The above novel thin film capacitor 1 with the improved top electrode105 may be fabricated as follows. The bottom electrode 102 is depositedon the semiconductor substrate 101. The high dielectric oxide layer 103is deposited on the bottom electrode 102. The top electrode 105 is thendeposited on the high dielectric oxide layer 103, wherein the first part104 a is deposited on the high dielectric oxide layer 103 at a lowerdeposition rate before the second part 104 b is deposited on the firstpart 104 a at a higher deposition rate. The first part 104 a and thesecond part 104 b are made of the same material such as Ru or Ir whichhas a high formability to the reactive ion etching. Howover, the firstpart 104 a in contact with the high dielectric oxide layer 103 isdeposited at a low deposition rate by applying the sputter target withthe low power level of not higher than 1.7 W/cm², whilst the second part104 b separated from the high dielectric oxide layer 103 is deposited ata high deposition rate by applying the sputter target with the highpower level of higher than 1.7 W/cm².

The conductive layer 104 may be deposited by any one of a sputteringmethod, a chemical vapor deposition method and an evaporation method,provided that the second deposition rate of the second part 104 b ishigher than the first deposition rate of the first part 104 a.

It is not essential for the present invention to limit the thickness ofthe first part 104 a in contact with the high dielectric oxide layer103. It is, however, preferable that the first part 104 a is very thin.The thickness of the first part 104 a is preferably not more than 10nanometers, and more preferably 5 nanometers.

It is also not essential for the present invention to limit thethickness of the second part 104 b separated from the high dielectricoxide layer 103. It is, however, preferable that the thickness of thesecond part 104 b is thicker by about ten times than the first part 104a.

The top electrode 105 further comprises a conductive layer 104 made of asingle conductive material which shows a formability to a reactive ionetching. The conductive layer 104 further comprises a first part 104 awhich has been deposited at a first deposition rate and a second part104 b which has been deposited on the first part 104 a at a seconddeposition rate which is higher than the first deposition rate. Thefirst part 104 a and the second part 104 b are made of the sameconductive material but are deposited at different deposition rates fromeach other so that the second deposition rate of the second part 104 bis higher than the first deposition rate of the first part 104 a. Afterthe above thin film capacitor 1 having the top electrode layer 104 issubjected to a heat treatment at 350° C., the above thin film capacitor1 shows a good leak current density characteristic such that the leakcurrent density remains suppressed at not higher than 1×10⁻⁸ A/cm² underapplication of a driving voltage in the range of 0V to 2V.

It is preferable that the conductive layer 104 includes at least any oneof Ru, RuO₂, Ir, IrO₂, and alloys thereof because those materials havehigh formability to the reactive ion etching. This allows a furthersubstantive scaling down of the thin film capacitor 1 with a highaccurate dimension to be defined by the reactive ion etching. Thisfurther substantive scaling down of the thin film capacitor 1 allows anincrease in density of integration of the semiconductor devices andintegrated circuits.

First, the above novel thin film capacitor has the good electriccharacteristics. The material of the first part in contact with the highdielectric oxide layer is deposited at a low deposition rate under a lowdeposition power to prevent reaction on the interface between the firstpart and the high dielectric oxide layer or prevent the top surface ofthe high dielectric oxide layer from receiving any substantive damage.

Second, the top electrode structure makes it possible to shorten thetime for deposition of the top electrode for improvement in throughputof the thin film capacitor. The first part is deposited at asufficiently low deposition rate for prevent the top surface of the highdielectric oxide layer from receiving any substantive damage, whilst thesecond part is deposited at a sufficiently high deposition rate forshortening a total time for depositions of the first and secondconductive layers.

Third, the first part intervening between the second part and the highdielectric oxide layer prevents peeling of the top electrode from thehigh dielectric oxide layer for improvement in the yield of the thinfilm capacitor.

Fourth, the material of the first and second parts are so selected as tohave a high formability to a reactive ion etching. The improvement informability of the top electrode allows a further scaling down of thethin film capacitor with a highly accurate dimension, whereby a furtherincrease in the degree of integration of the semiconductor devices canbe realized.

FIG. 2 is a fragmentary across sectional elevation view illustrative ofanother novel thin film capacitor with an improved top electrode inaccordance with the foregoing present inventions. A novel thin filmcapacitor 1 has the following structure. A bottom electrode layer 102 isprovided on a semiconductor substrate 101. A high dielectric oxide layer103 is provided on the bottom electrode layer 102. A top electrode 105is provided on the high dielectric oxide layer 103. The top electrode105 further comprises a first conductive layer 107 made of a firstconductive material which shows a formability to a reactive ion etchingand a second conductive layer 108 made of a second conductive materialwhich shows a formability to the reactive ion etching. The firstconductive layer 107 is formed on the high dielectric oxide layer 103and the second conductive layer 108 is formed on the first conductivelayer 107. The first conductive layer 107 is deposited at a firstdeposition rate and the second conductive layer 108 is deposited at asecond deposition rate which is higher than the first deposition rate.The first conductive layer 107 and the second conductive layer 108 aremade of different conductive materials from each other and are depositedat different deposition rates wherein the deposition rate of the secondconductive layer 108 is higher than the deposition rate of the firstconductive layer 107. After the above thin film capacitor 2 having thetop electrode layer 105 comprising the first conductive layer 107 andthe second conductive layer 108 is subjected to a heat treatment at 350°C., the above thin film capacitor 1 shows a good leak current densitycharacteristic such that the leak current density remains suppressed atnot higher than 1×10⁻⁸ A/cm² under application of a driving voltage inthe range of 0V to 2V.

It is preferable that the first conductive layer 107 includes at leastany one of Ru, RuO₂, Ir, IrO₂, and alloys thereof and the secondconductive layer 108 also includes at least other one of Ru, PuO₂, Ir,IrO₂, and alloys thereof because those materials have high formabilityto the reactive ion etching. This allows a further substantive scalingdown of the thin film capacitor 1 with a high accurate dimension to bedefined by the reactive ion etching. This further substantive scalingdown of the thin film capacitor 2 allows an increase in density ofintegration of the semiconductor devices and integrated circuits.

The first conductive layer 107 and the second conductive layer 108 maybe deposited by any one of a sputtering method, a chemical vapordeposition method and an evaporation methods provided that the seconddeposition rate of the second conductive layer 108 is higher than thefirst deposition rate of the first conductive layer 107.

When the sputtering method is applied to deposit the top electrode 105,the first conductive layer 107 is deposited by applying a target with afirst power and then the second conductive layer 108 is deposited byapplying the same target with a second power which is higher than thefirst power so that the second deposition rate of the second conductivelayer 108 is higher than the first deposition rate of the firstconductive layer 107.

It is not essential for the present invention to limit the power levelto be applied to the sputter target, but it is preferable to apply a lowpower level of, for example, 1.7 W/cm² to the sputter target for a lowrate deposition of the first conductive layer 107 in contact with thehigh dielectric oxide layer 103 in order to prevent the surface of thehigh dielectric oxide layer 103 from receipt of any substantive damage.In this case, the thin film capacitor shows the good current leakagecharacteristics such that the leak current density remains suppressed atnot higher than 1×10⁻⁸ A/cm² under applications to the target with thedriving voltage in the range of 0V to 2V. If, however, the sputtertarget is applied with a higher power level than 1.7 W/cm² for a highrate deposition of the first conductive layer 107 in contact with thehigh dielectric oxide layer 103 in order to provide the surface of thehigh dielectric oxide layer 103 from receipt of any substantive damage,then the thin film capacitor shows the undesirable current leakagecharacteristics such that the leak current density shows a rapidincrease from 1×10⁻⁸ A/cm² as the driving voltage to be applied to thetarget is increased from 1.5V. Consequently, it is preferable that thepower level applied to the sputter target for a low rate deposition oftic first conductive layer 107 in contact with the high dielectric oxidelayer 103 is suppressed at, for example, not higher than 1.7 W/cm².

Namely, it is preferable that the first voltage level applied to thetarget for a low rate deposition of the first conductive layer 107 isset not higher than 1.7 W/cm², whilst the second voltage level appliedto the target for a high rate deposition of the second conductive layer108 is set higher than 1.7 W/cm².

For example, the first conductive layer 107 is made of Ru which has ahigh formability to the reactive ion etching and the second conductivelayer 108 is made of Ir which also has a high formability to thereactive ion etching. Further, the first conductive layer 107 in contactwith the high dielectric oxide layer 103 is deposited at a lowdeposition rate by applying the sputter target with the low power levelof not higher than 1.7 W/cm², whilst the second conductive layer 108separated from the high dielectric oxide layer 103 is deposited at ahigh deposition rate by applying the sputter target with the high powerlevel of higher than 1.7 W/cm².

It is also preferable that a first thickness of the first conductivelayer 107 is much thinner than a second thickness of the secondconductive layer 108. For example, the first thickness of the firstconductive layer 107 is about one tenth of the second thickness of thesecond conductive layer 108.

The above novel thin film capacitor 2 with the improved top electrode105 may be fabricated as follows. The bottom electrode 102 is depositedon the semiconductor substrate 101. The high dielectric oxide layer 103is deposited on the bottom electrode 102. The top electrode 105 is thendeposited on the high dielectric oxide layer 103, wherein the firstconductive layer 107 is deposited on the high dielectric oxide layer 103at a lower deposition rate before the second conductive layer 108 isdeposited on the first conductive layer 107 at a higher deposition rate.The first conductive layer 107 is made of Ru which has a highformability to the reactive ion etching and the second conductive layer108 is made of Ir which also has a high formability to the reactive ionetching. Further, the first conductive layer 107 in contact with thehigh dielectric oxide layer 103 is deposited at a low deposition rate byapplying the sputter target with the low power level of not: higher than1.7 W/cm², whilst the second conductive layer 108 separated from thehigh dielectric oxide layer 103 is deposited at a high deposition rateby applying the sputter target with the high power level of higher than1.7 WV/cm².

The first conductive layer 107 and the second conductive layer 108 maybe deposited by any one of a sputtering method, a chemical vapordeposition method and an evaporation method, provided that the seconddeposition rate of the second conductive layer 108 is higher than thefirst deposition rate of the first conductive layer 107.

It is not essential for the present invention to limit the thickness ofthe first conductive layer 107 in contact with the high dielectric oxidelayer 103. It is, however, preferable that the first conductive layer107 is very thin. The thickness of the first conductive layer 107 ispreferably not more than 10 nanometers, and more preferably 5nanometers.

It is also not essential for the present invention to limit thethickness of the second conductive layer 108 separated from the highdielectric oxide layer 103. It is, however, preferable that thethickness of the first conductive layer 107 is thicker by about tentimes than the first conductive layer 107.

The top electrode 105 further comprises a first conductive layer 107made of a first conductive material which shows a formability to areactive ion etching and a second conductive layer 108 made of a secondconductive material which shows a formability to the reactive ionetching. The first conductive layer 107 is formed on the high dielectricoxide layer 103 and the second conductive layer 108 is formed on thefirst conductive layer 107. The first conductive layer 107 is depositedat a first deposition rate and the second conductive layer 108 isdeposited at a second deposition rate which is higher than the firstdeposition rate. The first conductive layer 107 and the secondconductive layer 108 are made of different conductive materials fromeach other and are deposited at different deposition rates wherein thedeposition rate of the second conductive layer 108 is higher than thedeposition rate of the first conductive layer 107. After the above thinfilm capacitor 2 having the top electrode layer 105 comprising the firstconductive layer 107 and the second conductive layer 108 is subjected toa heat treatment at 350° C., the above thin film capacitor 1 shows agood leak current density characteristic such that the leak currentdensity remains suppressed at not higher than 1×10⁻⁸ A/cm² underapplication of a driving voltage in the range of 0V to 2V.

It is preferable that tic first conductive layer 107 includes at leastany one of Ru, RuO₂, IT, IrO₂, and alloys thereof and the secondconductive layer 108 also includes at least other one of Ru, RuO₂, Ir,IrO₂, and alloys thereof because those materials have high formabilityto the reactive ion etching. This allows a further substantive scalingdown of the thin film capacitor 1 with a high accurate dimension to bedefined by the reactive ion etching. This further substantive scalingdown of the thin film capacitor 2 allows an increase in density ofintegration of the semiconductor devices and integrated circuits.

The above novel thin film capacitor provides the following advantages.

First, the above novel thin film capacitor has the good electriccharacteristics. The material of the first conductive layer in contactwith the high dielectric oxide layer is deposited at a low depositionrate under a low deposition power to prevent reaction on the interfacebetween the first conductive layer and the high dielectric oxide layeror prevent the top surface of the high dielectric oxide layer fromreceiving any substantive damage.

Second, the top electrode structure makes it possible to shorten thetime for deposition of the top electrode for improvement in throughputof the thin film capacitor. The first conductive layer is deposited at asufficiently low deposition rate for prevent the top surface of the highdielectric oxide layer from receiving any substantive damage, whilst thesecond conductive layer is deposited at a sufficiently high depositionrate for shortening a total time for depositions of the first and secondconductive layers.

Third, the first conductive layer intervening between the secondconductive layer and the high dielectric oxide layer prevents peeling ofthe top electrode from the high dielectric oxide layer for improvementin the yield of the thin film capacitor.

Fourth, the material of the first and second conductive layers are soselected as to have a high formability to a reactive ion etching. Theimprovement in formability of the top electrode allows a further scalingdown of the thin film capacitor with a highly accurate dimension,whereby a further increase in the degree of integration of thesemiconductor devices can be realized.

A first embodiment according to the present invention will be describedin detail with reference to FIG. 3 which is a fragmentary crosssectional elevation view illustrative of a novel thin film capacitorwith an improved top electrode structure in a first embodiment inaccordance with the present invention.

An n-type silicon substrate 11 having a resistivity of 0.1 Ωcm wasprepared. A bottom electrode 12 of RuO₂ having a thickness of 200nanometers was deposited on the silicon substrate 11 by a first DCsputtering method. An electron cyclotron resonance chemical vapordeposition method was carried out by use of Ba(DPM)₂, Sr(DPM)₂,Ti(i-OC₃H₇) and oxygen gases under conditions of a substrate temperatureof 500° C., a gas pressure of 7 mTorr, and a plasma excitation microwavepower of 500 W, thereby depositing a (Ba, Sr)TiO₃ high dielectric oxidelayer 13 with a thickness of 30 nanometers on the bottom electrode 12.

A second DC sputtering method was carried out under depositionconditions of a deposition temperature of 25° C., a gas pressure of 4mTorr, and a DC power of 0.6 W/cm₂, and a deposition rate of 5.6nanometers/min. thereby depositing an Ru first part 14 a with athickness of 5 nanometers on the (Ba, Sr)TiO₃ high dielectric oxidelayer 13.

The above second DC sputtering method was continued but under differentconditions of a deposition temperature of 25° C., a gas pressure of 4mTorr, and a DC power of 4.5 W/cm², and a deposition rate of 21nanometers/min. thereby depositing an Ru second part 14 b with athickness of 50 nanometers on the Ru first part 14 a. As a result, thenovel thin film capacitor was completed.

The Ru second part 14 b was deposited at the second deposition ratewhich is higher than the first deposition rate of the Ru first part 14 ain contact with the (Ba, Sr)TiO₃ high dielectric oxide layer 13 so as toshorten the deposition time necessary for forming the top electrode 15,thereby improving the throughput.

Thereafter, the novel thin film capacitor was placed in oxygen andnitrogen gases at a temperature of 350° C. for 30 minutes.

It was confirmed that the first deposition condition for depositing thefirst part 14 a contributes to suppress the pceling of the top electrode15 from the (Ba, Sr)TiO₃ high dielectric oxide layer 13. This results inimprovement in reliability of the thin film capacitor.

The adhesiveness was evaluated by varying the thickness of the the firstpart 104 a in the range of 5-20 nanometers. It was also confirmed thatthe adhesiveness is improved as the thickness of the first part 14 a ismade thin. The thickness of the first part 14 a is not more than 10nanometers, and preferably about 5 nanometers.

As a comparative embodiment, the conventional thin film capacitor havingthe single layered Ru top electrode deposited under the same depositionrate as the second part 14 b and at 1.7 W/cm² was prepared before theconventional thin film capacitor was also placed in oxygen and nitrogengases at a temperature of 350° C. for 30 minutes.

FIG. 5 is a diagram illustrative of variations in density of leakcurrent of the novel thin film capacitor with the improved top electrodestructure and the conventional thin film capacitor It was shown that theleak current characteristics of the novel thin film capacitor areremarkably improved as compared to the leak current characteristics ofthe conventional thin film capacitor.

As the driving voltage applied to the thin film capacitor is over 1.5V,the conventional thin film capacitor shows the undesirable currentleakage characteristics such that the leak current density shows a rapidincrease from 1×10⁻⁸ A/cm².

FIG. 5 apparently shows that when the prior art was applied, then thecurrent leakage characteristics of the conventional thin film capacitorare not good, for example, a leak current density of not less than1×10⁻⁶ A/cm² upon zero driving voltage application to the thin filmcapacitor Upon increase in the driving voltage to the thin filmcapacitor, the thin film capacitor shows a simple increase in the leakcurrent density. In contrast to the conventional thin film capacitor,the novel thin film capacitor with the improved double-layered topelectrode shows good current leakage characteristics, for example, a lowleak current density of not less than 1×10⁻⁸ A/cm² upon zero drivingvoltage application to the thin film capacitor. Upon increase in thedriving voltage from 0V to about 2V, the above low leak current densityalmost remains unchanged. For example, under the application of thedriving voltage of 2V to the novel thin film capacitor, the leak currentdensity remains not less than 1×10⁻⁸ A/cm². Namely, the novel thin filmcapacitor shows the stable and good leak characteristics.

The adhesiveness of the Pt first conductive layer 14 to the (Ba, Sr)TiO₃high dielectric oxide layer 13 was evaluated by varying the thickness ofthe Pt first conductive layer 14 in the range of 5-20 nanometers. It wasconfirmed that as the thickness of the Pt first conductive layer 14 isreduced, the adhesiveness of the Pt first conductive layer 14 to the(Ba, Sr)TiO₃ high dielectric oxide layer 13 is improved. For example, apreferable thickness range of the Pt first conductive layer 14 is notthicker than 10 nanometers. In contrast, the thin film capacitor showsthe good current leakage characteristics such that the leak currentdensity remains suppressed at not higher than 1×10⁻⁸ A/cm² underapplications to the target with the driving voltage in the range of 0Vto 3V.

Since the first part 14 a deposited at the low deposition rate is thin,it is possible to shorten the necessary time for depositing the topelectrode for improvement in throughput of the thin film capacitor.

As a modification to the above, the first part 14 a was deposited by anevaporation method. The thin film capacitor was then subjected to theevaluations in the leak current characteristics and adhesiveness. It wasconfirmed that the thin film capacitor shows the good leak currentcharacteristics and high adhesiveness.

As a further modification to the above, the first part 14 a wasdeposited by a chemical vapor deposition method. The thin film capacitorwas then subjected to the evaluations in the leak currentcharacteristics and adhesiveness. It was confirmed that the thin filmcapacitor shows the good leak current characteristics and highadhesiveness.

The above improved top electrode structure allows the thin filmcapacitor to have good leak current characteristics with high throughputand high yield conditions.

Available sputtering systems for depositing the electrodes of the novelthin film capacitor are not limited to a specific one. FIG. 6 is a blockdiagram illustrative of a structure of a sputtering system as oneexample of the available sputtering systems for depositing theelectrodes of the novel thin film capacitor. The sputtering system 20has a vacuum chamber 2 which accommodates a substrate holder 3 on whichsubstrates 4 arc mounted for forming a novel thin film capacitor. Thevacuum chamber 2 also accommodates a high frequency electrode plate 5with a sputter target 6 which faces to the substrates 4 on the substrateholder 3 and is distanced from the substrates 4 on the substrate holder3. It is of course possible to provide the high frequency electrodeplate 5 with plural different sputter targets 6. It is alternativelypossible to provide a plurality of the high frequency electrode plate 5so that different targets 6 arc provided on the plural high frequencyelectrode plates 5. A shutter 7 may optionally be provided between thesubstrate holder 3 and the high frequency electrode plate 5. An inertgas supplier 21 is further provided for supplying an inert gas into thevacuum chamber 2. A vacuum pump 22 is also provided for causing a vacuumof the vacuum chamber 2. A high frequency power supply 10 and a powercontroller 9 are provided for supplying a high frequency power throughthe power controller 9 to the high frequency electrode plate 5 undercontrol of the power, whereby the power controller 9 controls the powerto be applied to the target 6 on the high frequency electrode plate 5.Since the deposition rate depends on a voltage corresponding to thepower to be applied to the target 6, then the power controller 9controls the deposition rate. A control unit 8 is further provided whichis connected to both the vacuum pump 22 and the power controller 9 forcontrolling the deposition time of sputtering process and a degree ofthe vacuum in the vacuum chamber 2.

The above novel thin film capacitor with the improved double-layered topelectrode structure possesses the following advantages and effects.

First, the above novel thin film capacitor has the good electriccharacteristics. The material of the first part in contact with the highdielectric oxide layer is deposited at a low deposition rate under a lowdeposition power to prevent reaction on the interface between the firstpart and the high dielectric oxide layer or prevent the top surface ofthe high dielectric oxide layer from receiving any substantive damage.

Second, the top electrode structure makes it possible to shorten thetime for deposition of the top electrode for improvement in throughputof the thin film capacitor. The first part is deposited at asufficiently low deposition rate for prevent the top surface of the highdielectric oxide layer from receiving any substantive damage, whilst thesecond part is deposited at a sufficiently high deposition rate forshortening a total time for depositions of the first and secondconductive layers.

Third, the first part intervening between the second part and the highdielectric oxide layer prevents peeling of the top electrode from thehigh dielectric oxide layer for improvement in the yield of the thinfilm capacitor.

Fourth, the material of the first and second parts are so selected as tohave a high formability to a reactive ion etching. The improvement informability of the top electrode allows a further scaling down of thethin film capacitor with a highly accurate dimension, whereby a furtherincrease in the degree of integration of the semiconductor devices canbe realized.

The following descriptions will focus on possible modification to theabove present invention. In this embodiment, the bottom electrode ismade of RuO₂. Notwithstanding conductive materials are available for thebottom electrode, which are capable of keeping conductivity in an oxygenatmosphere during the process for formation of the high dielectric oxidelayer on the bottom electrode. For example, there are available for thebottom electrode material Ru, Ir, Re, Os, Rh, and oxides thereof as wellas at least any one selected from the group of silicide compounds inaddition at least any one selected from the group of Pt, Au, Ag, Pd, Ni,Co and alloys thereof.

Further, the bottom electrode may be modified to have multi-layerstructure.

In place of (Ba, Sr)TiO₃, materials represented by a chemical formulaABO₃ are available for the high dielectric oxide layer, wherein A maycomprise at least any one selected from the group consisting of Ba, Sr,Pb, Ca, La, Li and K, and B may comprise at least any one selected fromthe group consisting of Ti, Zr, Ta, Nb, Mg, Fe, Zn and W. For example,there are available SrTiO₃, (Sr, Ca)TiO₃, (Ba, Sr, Ca)TiO₃, PbTiO₃,Pb(Zr, Ti)O₃, (Pb, La)(Zr, Ti)O₃, Pb(Mg, Nb)O₃, Pb(Mg, W)O₃, Pb(Zn,Nb)O₃LiTaO₃, LiNbO₃, KTaO₃, KTaO₃, and kNb3. Further, there areavailable materials represented by the chemical formula(Bi₂O₂)(A_(m−1)B_(m)O_(3m+1))(m=1, 2, 3, 4, 5), wherein A may compriseat least any one selected from the group consisting of Ba, Sr, Pb, Ca, Kand Bi, and B may comprise at least any one selected from the groupconsisting of Nb, Ta, Ti, and W. For example, Ba₄Ti₃O₁₂, SrBa₂Ta₂O₉, andSrBa₂Nb₂O₉ are also available In addition, Ta₂O₅ is further availablewhich has a chemical composition different from those of the abovechemical formula

The above high dielectric oxide layer may be modified to have amulti-layered structure.

A second embodiment according to the present invention will be describedin detail with reference to FIG. 4 which is a fragmentary crosssectional elevation view illustrative of a novel thin film capacitorwith an improved top electrode structure in a first embodiment inaccordance with the present invention.

An n-type silicon substrate 11 having a resistivity of 0.1 Ωcm wasprepared. A bottom electrode 12 of RuO₂ having a thickness of 200nanometers was deposited on the silicon substrate 11 by a first DCsputtering method. An electron cyclotron resonance chemical vapordeposition method was carried out by use of Ba(DPM)₂, Sr(DPM)₂,Ti(iOC₃H₇) and oxygen gases under conditions of a substrate temperatureof 500° C., a gas pressure of 7 mTorr, and a plasma excitation microwavepower of 500 W, thereby depositing a (Ba, Sr)TiO₃ high dielectric oxidelayer 13 with a thickness of 30 nanometers on the bottom electrode 12.

A second DC sputtering method was carried out under depositionconditions of a deposition temperature of 25° C., a gas pressure of 4mTorr, and a DC power of 0.6 W/cm², and a deposition rate of 5.6nanometers/min. thereby depositing an Ru first conductive layer 17 witha thickness of 5 nanometers on the (Ba, Sr)TiO₃ high dielectric oxidelayer 13.

A third DC sputtering method was carried out under conditions of adeposition temperature of 25° C., a gas pressure of 4 mTorr, and a DCpower of 5.2 W/cm², and a deposition rate of 25 nanometers/min. therebydepositing an Ir second conductive layer 18 with a thickness of 50nanometers on the Ru first conductive layer 17. As a result, the novelthin film capacitor was completed.

The Ir second conductive layer 18 was deposited at the second depositionrate which is higher than the first deposition rate of the Ru firstconductive layer 17 in contact with the (Ba, Sr)TiO₃ high dielectricoxide layer 13 so as to shorten the deposition time necessary forforming the top electrode 15, thereby improving the throughput.

Thereafter, the novel thin film capacitor was placed in oxygen andnitrogen gases at a temperature of 350° C. for 30 minutes.

It was confirmed that the first deposition condition for depositing thefirst conductive layer 17 contributes to suppress the peeling of the topelectrode 15 from the (Ba, Sr)TiO₃ high dielectric oxide layer 13. Thisresults in improvement in reliability of the thin film capacitor.

The adhesiveness was evaluated by varying the thickness of the firstconductive layer 17 in the range of 5-20 nanometers. It was alsoconfirmed that the adhesiveness is improved as the thickness of thefirst conductive layer 17 is made thin. The thickness of the firstconductive layer 17 is not more than 10 nanometers, and preferably about5 nanometers

As a comparative embodiment, the conventional thin film capacitor havingthe single layered Ru top electrode deposited under the same depositionrate as the second conductive layer 18 and at 1.7 W/cm² was preparedbefore the conventional thin film capacitor was also placed in oxygenand nitrogen gases at a temperature of 350° C. for 30 minutes.

As the driving voltage applied to the thin film capacitor is over 1.5V,the conventional thin film capacitor shows the undesirable currentleakage characteristics such that the leak current density shows a rapidincrease from 1×10⁻⁸ A/cm².

When the prior art was applied, then the current leakage characteristicsof the conventional thin film capacitor are not good, for example, aleak current density of not less than 1×10⁻⁶ A/cm² upon zero drivingvoltage application to the thin film capacitor. Upon increase in thedriving voltage to the thin film capacitor, the thin film capacitorshows a simple increase in the leak current density. In contrast to theconventional thin film capacitor, the novel thin film capacitor with theimproved double-layered top electrode shows good current leakagecharacteristics, for example, a low leak current density of not lessthan 1×10⁻⁸ A/cm² upon zero driving voltage application to the thin filmcapacitor. Upon increase in the driving voltage from 0V to about 2V, theabove low leak current density almost remains unchanged. For example,under the application of the driving voltage of 2V to the novel thinfilm capacitor, the leak current density remains not less than 1×10⁻⁸A/cm². Namely, the novel thin film capacitor shows the stable and goodleak characteristics.

The adhesiveness of the Ru first conductive layer 17 to the (Ba, Sr)TiO₃high dielectric oxide layer 13 was evaluated by varying the thickness ofthe Ru first conductive layer 17 in the range of 5-20 nanometers. It wasconfirmed that as the thickness of the Ru first conductive layer 17 isreduced, the adhesiveness of the Ru first conductive layer 17 to the(Ba, Sr)TiO₃ high dielectric oxide layer 13 is improved, For example, apreferable thickness range of the Ru first conductive layer 17 is notthicker than 10 nanometers. In contrast, the thin film capacitor showsthe good current leakage characteristics such that the leak currentdensity remains suppressed at not higher than 1×10⁻⁸ A/cm² underapplications to the target with the driving voltage in the range of 0Vto 3V.

Since the first conductive layer 17 deposited at the low deposition rateis thin, it is possible to shorten the necessary time for depositing thetop electrode for improvement in throughput of the thin film capacitor.

As a modification to the above, the first conductive layer 17 wasdeposited by an evaporation method. The thin film capacitor was thensubjected to the evaluations in the leak current characteristics andadhesiveness. It was confirmed that the thin film capacitor shows thegood leak current characteristics and high adhesiveness.

As a further modification to the above, the first conductive layer 17was deposited by a chemical vapor deposition method. The thin filmcapacitor was then subjected to the evaluations in the leak currentcharacteristics and adhesiveness. It was confirmed that the thin filmcapacitor shows the good leak current characteristics and highadhesiveness.

The above improved top electrode structure allows the thin filmcapacitor to have good leak current characteristics with high throughputand high yield conditions.

Available sputtering systems for depositing the electrodes of the novelthin film capacitor are not limited to a specific one. The sputteringsystem 20 has a vacuum chamber 2 which accommodates a substrate holder 3on which substrates 4 are mounted for forming a novel thin filmcapacitor. The vacuum chamber 2 also accommodates a high frequencyelectrode plate 5 with a sputter target 6 which faces to the substrates4 on the substrate holder 3 and is distanced from the substrates 4 onthe substrate holder 3. It is of course possible to provide the highfrequency electrode plate 5 with plural different sputter targets 6. Itis alternatively possible to provide a plurality of the high frequencyelectrode plate 5 so that different targets 6 are provided on the pluralhigh frequency electrode plates 5. A shutter 7 may optionally beprovided between the substrate holder 3 and the high frequency electrodeplate 5. An inert gas supplier 21 is further provided for supplying aninert gas into the vacuum chamber 2. A vacuum pump 22 is also providedfor causing a vacuum of the vacuum chamber 2. A high frequency powersupply 10 and a power controller 9 are provided for supplying a highfrequency power through the power controller 9 to the high frequencyelectrode plate 5 under control of the power, whereby the powercontroller 9 controls the power to be applied to the target 6 on thehigh frequency electrode plate 5. Since the deposition rate depends on avoltage corresponding to the power to be applied to the target 6, thenthe power controller 9 controls the deposition rate. A control Unit 8 isfurther provided which is connected to both the vacuum pump 22 and thepower controller 9 for controlling the deposition time of sputteringprocess and a degree of the vacuum in the vacuum chamber 2.

The above novel thin film capacitor with the improved double-layered topelectrode structure possesses the following advantages and effects.

First, the above novel thin film capacitor has the good electriccharacteristics. The material of the first conductive layer in contactwith the high dielectric oxide layer is deposited at a low depositionrate under a low deposition power to prevent reaction on the interfacebetween the first conductive layer and the high dielectric oxide layeror prevent the top surface of the high dielectric oxide layer fromreceiving any substantive damage.

Second, the top electrode structure makes it possible to shorten thetime for deposition of the top electrode for improvement in throughputof the thin film capacitor. The first conductive layer is deposited at asufficiently low deposition rate for prevent the top surface of the highdielectric oxide layer from receiving any substantive damage, whilst thesecond conductive layer is deposited at a sufficiently high depositionrate for shortening a total time for depositions of the first and secondconductive layers.

Third, the first conductive layer intervening between the secondconductive layer and the high dielectric oxide layer prevents peeling ofthe top electrode from the high dielectric oxide layer for improvementin the yield of the thin film capacitor.

Fourth, the material of the first and second conductive layers are soselected as to have a high formability to a reactive ion etching. Theimprovement in formability of the top electrode allows a further scalingdown of the thin film capacitor with a highly accurate dimension,whereby a further increase in the degree of integration of thesemiconductor devices can be realized.

The following descriptions will focus on possible modification to theabove present invention. In this embodiment, the bottom electrode ismade of RuO₂. Notwithstanding, conductive materials are available forthe bottom electrode, which are capable of keeping conductivity in anoxygen atmosphere during the process for formation of the highdielectric oxide layer on the bottom electrode. For example, there areavailable for the bottom electrode material Ru, Ir, Rc, Os, Rh, andoxides thereof as well as at least any one selected from the group ofsilicide compounds in addition at least any one selected from the groupof Pt, Au, Ag, Pd, Ni, Co and alloys thereof.

Further, the bottom electrode may be modified to have multilayerstructure.

In place of (Ba, Sr)TiO₃, materials represented by a chemical formulaABO₃ are available for the high dielectric oxide layer, wherein A maycomprise at least any one selected from the group consisting of Ba, Sr,Pb, Ca, La, Li and K, and B may comprise at least any one selected fromthe group consisting of Ti, Zr, Ta, Nb, Mg, Fe, Zn and W. For example,there are available SrTiO₃, (Sr, Ca)TiO₃, (Ba, Sr, Ca)TiO₃, PbTiO₃,Pb(Zr, Ti)O₃, (Pb, La)(Zr, Ti)O₃, Pb(Mg, Nb)O₃, Pb(Mg, W)O₃, Pb(Zn,Nb)O₃LiTaO₃, LiNbO₃, KTaO₃, KTaO₃, and KNbO₃. Further, there areavailable materials represented by the chemical formula(Bi₂O₂)(A_(m−1)B_(m)O_(3m +1)) (m=1, 2, 3, 4, 5), wherein A may compriseat least any one selected from the group consisting of Ba, Sr, Pb, Ca, Kand Bi, and B may comprise at least any one selected from the groupconsisting of Nb, Ta, Ti, and W. For example, Ba₄Ti₃O₁₂, SrBa₂Ta₂O₉, andSrBa₂Nb₂O₉ are also available. In addition, Ta₂O₅ is further availablewhich has a chemical composition different from tliose of the abovechemical formula.

The above high dielectric oxide layer may be modified to have amulti-layered structure.

Whereas modifications of the present invention will be apparent to aperson having ordinary skill in the art, to which the inventionpertains, it is to be understood that embodiments as shown and describedby way of illustrations are by no means intended to be considered in alimiting sense. Accordingly, it is to be intended to cover by claims allmodifications which fall within the spirit and scope of the presentinvention.

What is claimed is:
 1. A multi-layer structure comprising: a highdielectric oxide layer; a first conductive layer on said high dielectricoxide layer, and said first conductive layer processing a highformability to a reactive ion etching; and a second conductive layer onsaid first conductive layer, and said second conductive layer processinga high formability to said reactive ion etching, wherein an interfacebetween said first conductive layer and said high dielectric oxide layeris such that a density of a leak current across said interface issuppressed at not higher than 1×10⁻⁸ A/cm² upon applying a voltage of 2Vacross said dielectric oxide layer after said multi-layer structure hasbeen subjected to a heat treatment at 350° C.
 2. The multi-layerstructure as claimed in claim 1, wherein said first conductive layer andsaid second conductive layer are made of the same conductive materialwhich includes at least any one selected from the group consisting ofRu, RuO₂, Ir, IrO₂, and alloys thereof.
 3. The multi-layer structure asclaimed in claim 1, wherein said first conductive layer and said secondconductive layer are made of different conductive materials, each ofwhich includes at least any one selected from the group consisting ofRu, RUO₂, Ir, IrO₂, and alloys thereof.
 4. The multi-layer structure asclaimed in claim 3, wherein said first conductive layer consistsessentially of Ru and said second conductive layer consists essentiallyof Ir.
 5. The multi-layer structure as claimed in claim 1, wherein saidfirst conductive layer has a thickness of about one-tenth of a thicknessof said second conductive layer.
 6. A top electrode structure of a thinfilm capacitor, said structure comprising: a first conductive layer on ahigh dielectric oxide layer, and said first conductive layer processinga high formability to a reactive ion etching; and a second conductivelayer on said first conductive layer, and said second conductive layerprocessing a high formability to said reactive ion etching, wherein aninterface between said first conductive layer and said high dielectricoxide layer is such that a density of a leak current across saidinterface is suppressed at not higher than 1×10⁻⁸ A/cm² upon applying avoltage of 2V across said dielectric oxide layer after said multi-layerstructure has been subjected to a heat treatment at 350° C.
 7. The topelectrode structure as claimed in claim 6, wherein said first conductivelayer and said second conductive layer are made of the same conductivematerial which includes at least any one selected from the groupconsisting of Ru, RuO₂, Ir, IrO₂, and alloys thereof.
 8. The topelectrode structure as claimed in claim 6, wherein said first conductivelayer and said second conductive layer are made of different conductivematerials, each of which includes at least any one selected from thegroup consisting of Ru, RuO₂, Ir, IrO₂, and alloys thereof.
 9. The topelectrode structure as claimed in claim 8, wherein said first conductivelayer consists essentially of Ru and said second conductive layerconsists essentially of Ir.
 10. The top electrode structure as claimedin claim 6, wherein said first conductive layer has a thickness of aboutone-tenth of a thickness of said second conductive layer.